Determination of Hexavalent Chromium Cr(VI) in Drinking Water by Suppressed Conductivity Detection

Significance of the topic

Accurate quantification of hexavalent chromium (Cr(VI)) in drinking water is critical due to its high toxicity and carcinogenic potential compared to trivalent chromium. Regulatory agencies have set stringent limits (e.g., California PHG of 0.020 µg/L and MCL of 10 µg/L), driving the need for sensitive, robust analytical methods.

Objectives and Study Overview

This work aims to develop a direct ion chromatography method with suppressed conductivity detection to determine Cr(VI) in drinking water at regulatory levels. The approach removes the need for postcolumn derivatization and leverages hydroxide eluents for improved sensitivity.

Instrumentation

• Thermo Scientific Dionex ICS-5000+ HPIC system with dual pump, RFIC eluent generator (EGC 500 KOH cartridge), and DC detector compartment
• Dionex AS-AP autosampler with 5 mL syringe, optimized for push-full injections
• Dionex IonPac AG11-HC guard and AS11-HC or AG11-HC-4 µm guard and AS11-HC-4 µm analytical columns
• Dionex AERS 500 electrolytic suppressor in recycle mode and CR-ATC 500 anion trap column
• Chromeleon CDS software for sequence control and data analysis

Methodology

Samples and standards were adjusted with ammonium hydroxide/ammonium sulfate buffer and spiked into simulated high-ionic-strength water (HIW) containing common anions. An isocratic elution with 45 mM KOH at 0.38 mL/min and 30 °C was used. A 300 µL injection volume with loop overfill factor 5 ensured low detection limits. Suppressed conductivity detection yielded water as the suppression product, reducing baseline conductance.

Results and Discussion

Chromate elutes at ~8.6 min on both AS11-HC and AS11-HC-4 µm columns, with minor retention shifts in HIW matrices. Calibration was linear from 1 to 30 µg/L (r^2 > 0.9993). Detection limits in DI water were as low as 0.17 µg/L (LOD) and 0.58 µg/L (LOQ) on the 4 µm column. Method detection limits (MDL) in HIW were ~0.35–0.53 µg/L, and lowest-concentration minimum reporting limits (LCMRL) were 1.2–2.2 µg/L. Spike recoveries in HIW and tap water ranged from 80–110%, except one low-level HIW spike on the 2 µm column. These figures demonstrate reliable performance at or below the 10 µg/L regulatory threshold.

Benefits and Practical Applications

The direct suppressed conductivity method simplifies workflow by eliminating derivatization reagents and reduces background noise relative to carbonate eluents. It meets drinking water compliance requirements and can be implemented on existing RFIC platforms, making it ideal for routine monitoring in environmental and QA/QC laboratories.

Future Trends and Applications

Advances may include microbore or capillary columns for further sensitivity, integration with mass spectrometry for speciation, on-line sample cleanup to extend column life, and portable IC systems for field analyses. Continuous suppressor innovations and automated calibration/calculation tools will enhance reliability and ease of use.

Conclusion

This study presents a robust ion chromatography approach with suppressed conductivity detection for Cr(VI) in drinking water. The method achieves sub-µg/L detection limits, linear quantitation across relevant ranges, and satisfactory recoveries, fulfilling regulatory demands without complex postcolumn chemistry.

References

1. Bielicka A, Bojanowska I, Wisniewski A. Two Faces of Chromium – Pollutant and Bioelement. Pol J Environ Stud. 2005;14(1):5–10.
2. U.S. EPA. Toxicological Review of Trivalent Chromium. 1998.
3. U.S. EPA. Toxicological Review of Hexavalent Chromium. 1998.
4. Cieslak-Golonka M. Toxic and Mutagenic Effects of Chromium(VI) – A Review. Polyhedron. 1995;15(21):3667–3918.
5. U.S. EPA. Drinking Water Contaminants. 2014.
6. U.S. EPA. Basic Information about Chromium in Drinking Water. 2013.
7. California OEHHA. Public Health Goal for Chromium in Drinking Water. 1999.
8. California OEHHA. Public Health Goal for Hexavalent Chromium in Drinking Water. 2010.
9. U.S. EPA. Method 218.7: Determination of Hexavalent Chromium in Drinking Water by IC with Postcolumn Derivatization and UV-Visible Detection. 2011.
10. U.S. EPA. Method 218.6: Determination of Dissolved Hexavalent Chromium by IC. 1991.
11. Thermo Scientific. Application Update 144: Determination of Hexavalent Chromium in Drinking Water Using IC. 2003.
12. Thermo Scientific. Technical Note 26: Determination of Cr(VI) in Water, Waste Water, and Solid Waste Extracts. 1998.
13. California Department of Public Health. State Adoption of Hexavalent Chromium MCL. 2014.
14. Thermo Scientific. Application Update 179: Sensitive Determination of Hexavalent Chromium in Drinking Water. 2012.
15. Thermo Scientific. Application Update 133: Determination of Inorganic Anions in Drinking Water by IC. 2004.
16. U.S. EPA. Lowest Concentration Minimum Reporting Level (LCMRL). 2013.